With the trend of electronic communication devices becoming lighter, thinner, shorter, smaller and multifunctional, as well as acceleration of data transmission speed, electronic devices assembled inside electronic products need to be accordingly of high integration, high assembly density and low production cost. If it is necessary to achieve high transmission speed in small devices, the EMI is a problem that needs to be solved.
In the products such as notebook, LCD display, USB and so forth, laminated high-current chip beads are utilized to suppress EMI that is designed to be close to power cords of the products. In case of in-phase current (i.e. common mode current), due to overlapping magnetic fluxes, impedance will be generated for eliminating noise. On the other hand, when reverse current passes (i.e. normal mode), the generated magnetic fluxes cancel each other, and thus no impedance is created. Using the characteristic impedance of ferrite material with frequency to reduce the radiated noise is a cheap and commonly used device for EMI.